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Designing Detention Pond

Pond Design by Time-area Method #

Click Add in Project View to create a new MSMA project. Choose Pond, select MSMA 2nd Edition, create the name of the project, select the method to be used and click Create. Method used in section 3.1 is Time-Area Method. 

Pre-development #

Calculate pre-development discharge by inputting data in Pre tab. Pond design can also be integrated from drainage if the analysis of drainage has been carried out. 

  1. Input or select location. The location can be input by entering the location of Longitude and Latitude. Click “Use” button to use the proposed nearest raingauge location. The Location can also be selected by clicking on Raingauge Location drop list.
  1. The fitting constants are generated automatically and it is editable. Click on button to change the fitting constants to default value based on selected location.

  1. Input length of flow path from catchment divide to outlet, slope of stream flow path and catchment area to obtain tc and it is editable.

  1. Select Minor and Major Design ARI. Rainfall intensity is generated automatically.

  1. Select Region from the drop list.

  1. Click the “ Calculate” button to obtain Minor and Major Storm discharge.

Post-development #

Calculate post-development discharge by inputting data in the Post tab.

  1. Input overland sheet flow path length, slope of overland surface and manning coefficient to obtain to.
  1. Inputs drain flow length and average velocity to obtain td and  tc.
  1. Input total catchment and define the sub-catchments for pervious and impervious areas.
  1. Click the “ Calculate” button to obtain post-development critical storm duration.

Pond Sizing #

Determine required storage by inputting data in the Pond Sizing tab. Pond sizing design can be synchronized with Pond Platform. Pond platform can be assigned in EW modules (Platform > Spread Input > Type Column > Assign the platform as Pond).

  1. Select the Pond Type.
  1. Input the dimension of the pond such as top length, top width, depth, side slope, invert level and etc. to calculate the volume.
  1. The graphical pond displayed can be rotated to different views.
  1. Click the “ Calculate” button to obtain the volume and pond top area.

Outlet Design #

Design the outlet by inputting data in the Outlet Design tab.

  1. Minor Design Storm Primary Outlet

a. Input orifice height between pond and orifice invert level, H.

b. Choose orifice type 

c. Input orifice diameter, Do and number of orifice.

d. Click “ Routing” to obtain “Maximum Water Level”.

e. Post-development storm outlet maximum discharge must be lower than pre-development minor design storm peak flow.

  1. Major Design Storm Primary Outlet

a. Major storm primary outlet design is optional. Untick the box to exclude major design storm primary outlets.

b. Input orifice height between pond and orifice invert level, H. H for Major Design must be higher than “Maximum Water Level of Minor Design – Pond Invert Level”.

c. Select orifice type

d. Input orifice diameter, Do and number of orifice.

e. Click “ Routing” to obtain “Maximum Water Level”

f. Post-development major design storm outlet maximum discharge must be lower than pre-development major design storm peak flow.

  1. Secondary Outlet Arrangement

a. Input weir height between pond and spillway invert level, H. H for Secondary outlet must be higher than “Maximum Water Level of Major Design – Pond Invert Level”.

b. Input weir width.

c. Select ARI.

d. Click “ Routing” to obtain “Maximum Water Level”.

Note: “Input is not completed” message pops out if the Routing button is not clicked. Therefore, the Routing tab must be clicked before analyzing. Such message is as below. 

Result #

Click the “ Analyse” button to generate textual report, summary report, graph, and water level profile.

Water Level Simulation will be shown for every 5 minutes interval.

Click Textual Report, Summary Report, Graph, Appendix or Water Level Profile tabs to show the outcomes respectively.

Pond Design by Rational Method  #

Click Add in Project View to create a new MSMA project. Choose Pond, select MSMA 2nd Edition, create the name of the project, select the method to be used and click Create. Method used in section 3.2 is Rational Method. 

Pre-development #

Calculate pre-development discharge by inputting data in Pre tab. Pond design can also be integrated from drainage if the analysis of drainage has been carried out. 

  1. Input or select location. The location can be input by entering the location of Longitude and Latitude. Click “Use” button to use the proposed nearest raingauge location. The Location also can be selected by clicking on the Raingauge Location drop list.

  1. The fitting constants are generated automatically and it is editable. Click on button to change the fitting constants to default value based on selected location.

  1. Input length of flow path from catchment divide to outlet, slope of stream flow path and catchment area to obtain tc and it is editable.

  1. Select Minor, Major and Secondary Outlet design storm ARI. Rainfall intensity is generated automatically.

  1. Select appropriate Land Use for impervious and pervious areas. Users can click on the button ‘+’ or ‘-’ and the right side of the table to add or delete a number of rows from the table. Then key in area to each specified land use respectively.

  1. Click the “ Calculate” button to obtain Minor, Major and Secondary Outlet design storm peak flow.

Post-development #

Calculate post-development discharge by inputting data in the Post tab.

  1. Input overland sheet flow path length, slope of overland surface and manning coefficient to obtain to.

  1. Inputs drain flow length and average velocity to obtain td and  tc.

  1. Select appropriate Land Use for impervious and pervious areas. Users can click on the button ‘+’ or ‘-’ and the right side of the table t o add or delete a number of rows from the table. Then key in area to each specified land use respectively.

  1. Click the “ Calculate” button to obtain post-development preliminary critical storm duration and respective peak flows for each storm event.

  1. Cells in light blue color indicate the value is editable. The edited cell’s frame will be highlighted in red color.

Pond Sizing #

Determine required storage by inputting data in the Pond Sizing tab. Pond sizing design can be synchronized with Pond Platform. Pond platform can be assigned in EW modules (Platform > Spread Input > Type Column > Assign the platform as Pond)

  1. Select the type of the pond.
  1. Input the pond dimension to calculate the volume. 
  1. The graphical pond displayed can be rotated to different views.
  1. Click the “ Calculate” button to obtain the volume and pond top area.

Outlet Design #

Design the outlet by inputting data in the Outlet Design tab.

  1. Minor Design Storm Primary Outlet

a. Input orifice height between pond and orifice invert level, H.

b. Select orifice type

c. Input orifice diameter, Do and number of orifice.

d. Click “ Routing” to obtain “Maximum Water Level”.

e. Post-development storm outlet maximum discharge must be lower than pre-development minor design storm peak flow.

  1. Major Design Storm Primary Outlet

a. Major storm primary outlet design is optional. Untick the box to exclude major design storm primary outlets.

b. Input orifice height between pond and orifice invert level, H. H for Major Design must be higher than “Maximum Water Level of Minor Design – Pond Invert Level”.

c. Select orifice type

d. Input orifice diameter, Do and number of orifice.

e. Click “ Routing” to obtain “Maximum Water Level”

f. Post-development major design storm outlet maximum discharge must be lower than pre-development major design storm peak flow.

  1. Secondary Outlet Arrangement

a. Input weir height between pond and spillway invert level, H. H for Secondary outlet must be higher than “Maximum Water Level of Major Design – Pond Invert Level”.

b. Input weir width.

c. Click “ Routing” to obtain “Maximum Water Level”.

Result #

Click the “ Analyse” button to generate the result.

Water Level Simulation will be shown for every 5 minutes interval.

Click Textual Report, Summary Report, Graph, Appendix or Water Level Profile tabs to view the results.

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